1. Field of the Invention
The present invention relates to a circuit arrangement for providing a slow, constant forward/reverse movement of the write/read heads in a cylinder memory, and more particularly to such an arrangement in association with a regulating circuit which comprises a track difference register, a digital/analog coverter connected to the register and an arrangement for providing a sign to the analog signal, and a function generator for receiving the analog signal.
2. Description of the Prior Art
A positioning system for the write/read heads of a cylinder memory must fulfill two basic functions. First of all the system must be able to find new data tracks in the shortest possible time and, secondly, the system must be able to precisely position the heads on the data tracks during a reading process or a writing process.
Therefore, conventionally two regulating circuits have been provided, i.e. a coarse regulating circuit intermeshed with a fine regulating circuit. The coarse regulating circuit contains a path-dependent speed control of the positioning unit, and the path to be traveled to the new target track is stored, as a binary track difference (cylinder difference) in a difference register. The track difference register is caused to count backward with the cylinder pulses of the intersecting tracks. A digital/analog converter produces an analog value from the particular digital value. Depending upon the position of the target track, the analog value is then provided, by way of a forward/reverse circuit, with an appropriate sign, and with the aid of a function generator is distorted to form the theoretical speed signal. At the input of a summing amplifier the theoretical speed signal and the actual speed signal are compared with one another, the difference is amplified, and the amplified difference is fed to a power amplifier which operates the positioning device. A so-called "smoother" serves, in a manner well known in the art, to smooth the output function of the digital/analog converter.
The fine regulation system is responsible for the position of the data heads on the theoretical track. It is activated as soon as the difference register is caused to count back to zero at the end of a positioning process. Here, the regulating value "path" is represented by the analog position error signal. In modern disc memories, the signal is derived from a special servo surface of the stack of discs. The position error signal is amplified in the summing amplifier and, by way of the power amplifier, causes the positioning drive unit to move in the direction in which the error signal becomes zero.
In addition to the two above described basic functions, the position regulating device of a cylinder memory must also handle a series of subsidiary functions including the function of "slow, constant forward and/or backward movement of the write/read heads".
In known cylinder memories, special digital/analog circuits which supply a constant theoretical speed value are provided for the slow forward/reverse movement. As it is also necessary to provide a sign formation for both directions of movement, the expense for such additional circuitry is considerable.